The present invention relates to an image processing apparatus and an image processing method of coding an image.
Natural images such as photographs are sometimes synthesized with characters and compressed by coding. In this processing, a character pattern corresponding to characters to be synthesized is read out from a font memory, synthesized on a natural image stored in an image memory, and coded by, e.g., JPEG coding. If the font is especially small, it is enlarged before being synthesized.
In the above conventional method, however, since the JPEG coding performs coding in units of 8.times.8 blocks, a character crosses coding blocks depending on the enlargement ratio of a font to be synthesized or on the position of synthesis. This increases high-frequency components in the blocks or increases asymmetry between the blocks, giving rise to a block distortion unique to the JPEG coding.
Also, since character images contain a large amount of high-frequency components, the code length of a character image tends to increase in comparison with the simplicity of the image. Unfortunately, the JPEG coding performs irreversible coding by cutting off high-frequency components, and so the image quality of particularly a character image deteriorates.